The present invention relates to a machine for making filter bags for products for infusion, such as tea, coffee, chamomile, etc.
In the present description, the filter bags made are of the so-called two-lobe type, with the thread and pick-up tab connected by part of a heat-sealable adhesive seal, located over one end of the filter bag, whilst another part of the seal is used to join one end of the thread to a heat-sealed edge of one lobe of the filter bag (opposite that on which the pick-up tab is joined). The thread, whose length is substantially equal to the total length of the two extended lobes, is wrapped around the filter bag.
Automatic packaging machines which make the above-mentioned filter bags normally comprise: a first station which feeds a continuous web of filter paper under a station which delivers successive doses of the product for infusion at given intervals; a sealing station which uses longitudinal and transversal heat-sealing to form a continuous flat tubular envelope, with a continuous succession of lobes containing doses of the product.
This continuous tube is fed as far as an operating station at which a continuous thread with pick-up tabs attached at regular intervals and the relative seals, is fixed to the continuous tube by heat-sealing the seals to the tube.
Following application of the thread with the pick-up tab and seal, successive operating stations cut the continuous tube transversally into portions, each with a pair of lobes, fold each pair of lobes towards one another and join them in such a way as to form a two-lobe filter bag.
The station which applies the seal and pick-up tab to the thread (of particular interest in this description), comprises a rotary drum with continuous motion, located below the surface on which the continuous tube of lobes passes and having a plurality of seats evenly distributed over its surface. These comprise vacuum means which pick up the thread, tabs and seals and a heating base, designed to join the seals to the thread and the tabs.
As described and illustrated, for example, in Italian Patent No. 1.207.629, close to the drum, one upstream of the other relative to the direction of rotation of the drum, there is a unit which feeds one seal at a time to a relative seat and a unit which feeds one pick-up tab at a time to the same seat. Between the two units there is a unit which feeds the continuous thread over the drum. The distance between two successive vacuum seats is equal to the total length of two lobes of a filter bag. The synchronized feed of the three elements (thread, pick-up tab and seal joined together) allows them to be brought to the continuous tubular envelope at a zone in which there is a counter-roller which is heated and designed to allow fixing of the sealxe2x80x94pick-up tab and thread to the continuous tube.
The unit which feeds the seal to the rotary drum comprises means for feeding a continuous web, which is fed intermittently to a cutting roller fitted with a knife which operates in conjunction with a fixed blade to form individual seals, by means of two successive cuts in the continuous web which form a front end and a rear end of the seal. The cutting roller is positioned at a tangent to the rotary drum so that, during formation of the rear end of the seal by the knife and the fixed blade, the front end of the seal is picked up by the drum seat by means of the vacuum.
Similarly, the unit which feeds the pick-up tabs comprises means which feed a continuous web, which is fed with intermittent motion to a cutting roller having a knife which, operating in conjunction with a fixed blade, cuts the continuous web into sections, each forming a single pick-up tab, by means of two successive cuts in the continuous web which form a front end and a rear end of the pick-up tab. Similarly, the cutting roller is positioned at a tangent to the rotary drum so that, during formation of the rear end of the pick-up tab by the knife and fixed blade, the front end of the pick-up tab is picked up by the drum seat by means of the vacuum.
In recent years, the continuous studies which aimed to make packaging machines more productive have brought a significant increase in the operating speed of the individual parts of the various operating stations.
In particular, the increase in the speed of rotation of the drum has resulted in significant disadvantages.
In fact, it has been observed that, due to the increased speed of rotation of the drum, the transfer of the seals and pick-up tabs from the cutting rollers to the vacuum seats on the drum does not occur correctly. As a result, the pick-up tab and seal are often incorrectly positioned on the tubular envelope and, therefore, on the filter bags.
In other words, the seal and/or pick-up tab are often picked up in an uncontrolled fashion by the rotary drum which turns at high speed, being subjected to xe2x80x9cjerkingxe2x80x9d during the transit of the seal and/or pick-up tab from the cutting roller to the drum vacuum seat, such that it results in incorrect positioning on the vacuum seat.
The aim of the present invention is, therefore, to overcome the above-mentioned disadvantages.
Accordingly, the present invention provides a packaging machine for making filter bags for products for infusion. These filter bags are made from a flat tubular filter paper envelope containing a succession of doses of the product for infusion. Each filter bag has a connecting thread and a pick-up tab, joined to one another and to the filter bag by a seal made of a heat-sealable material. The packaging machine comprises at least a station which uses heat-sealing to apply the continuous thread on the lower surface of the flat tubular envelope, the continuous thread bearing the seal and pick-up tab. This application station comprises a first drum, rotating in a given direction, positioned at a tangent to the tubular envelope, the outer surface of the drum having a plurality of seats which retain the seals, thread and pick-up tabs which are fed from relative feed units, each unit being positioned downstream of the next relative to the direction of rotation. The feed units for the seals and pick-up tabs comprise respective units which feed corresponding webs to elements that cut the webs so as to form individual seals and individual pick-up tabs. The machine is characterized in that the seal and pick-up tab feed units also comprise transfer means, operating between the cutting elements and the drum, which pick up the individual seals and individual pick-up tabs at a first zone at the cutting elements and transfer them to a second zone, separated from the first zone by a given angle, opposite a seat on the drum.